Why is sleep mode not affecting my video card fan?

I run Vista 64 bit. Sometimes when I put my computer in sleep mode my video card fan won't stop running. Any suggestions?|||The only thing I can think of is upgrade to Windows 7. It has better sleep and hibernate, as in it actually works great, better than vista|||yeah your video card is still hot and cooling down. the board has a temp sensor in it even in sleep mode it will run the fan to cool it off. you don't want to over heat the cpu in the video card and burn it out do ya